Which episode of Lin Beixing knows the truth?

In Twinkle, Twinkle, Bright Stars, episode 19 of Lin Beixing knows the truth.

Episode 19: Zhang Wansen recorded his regretful love for Lin Beixing in his diary word by word, and this event is the moment when Lin Beixing was able to return to the past. At this time, she realized that every text message that made her go back was a moment of Zhang Wansen's regret.

After reading the diary, Lin Beixing walked by the familiar seaside, and she regretted whether they wouldn't have so many regrets if she could look back then. She also found that the end of time and space was not Zhang Wansen's death, but that they said to each other, I like you.

Synopsis

The drama tells that Lin Beixing, who is overbearing and loving, gave up her self following love, but was heartbroken by her boyfriend's abandonment. When she was packing things related to her ex-boyfriend, she triggered a special function because of deleting short messages in her mobile phone, and began to travel back to high school frequently, but she was always forced to pull back to the real world at the best time.

After several explorations, Lin Beixing found that the key to crossing lies in Zhang Wansen, so he decided to make friends with Zhang Wansen and make it complete. On the way to save themselves and Zhang Wansen, they had frequent contact and produced emotions. On the road of growing up together, there was a story of redemption and romantic love.